German Patent Application No. 29 22 160 describes a wiper system for operating the wipers of motor vehicles in which a correcting quantity characterizing wiper deceleration after turning off the operating switch or deactivating the motor is derived from a switching signal characterizing the angular velocity of the motor in an evaluation circuit. Taking this correcting quantity into account, the evaluation circuit emits a switching signal while the wiper is in different angular positions in order to place the wiper in a parking position as soon as the operating switch is turned off.
Using a rotational speed sensor having a first counter and a clock generator having a second counter, this arrangement starts counting from the time the wiper enters a parking zone until the counts of both counters are identical. The switching signal is then emitted for deactivating the motor. The wiper motor is deactivated earlier at high wiping speeds than at lower wiping speeds.
The disadvantage of this arrangement is that it always measures the wiping speed in a region (or parking zone) prior to the parking position or before the motor is deactivated. In addition, wiper motion is no longer detected after the motor is deactivated. This means that the wiper system dynamics are measured while the motor is energized. However, local wetness conditions on the windshield are variable. This makes it difficult to maintain the parking position solely by deriving the correcting quantity from the angular velocity of the motor.
A further disadvantage of this arrangement is that this wiper system merely places the wipers in the parking position. It does not enable the wipers to maintain the reversing positions during operation.
The use of a contact disc and a rotational speed sensor, which make the arrangement more expensive, is another disadvantage.